I am posting my answer to your question also here in order to contribute to our community.
Please note that we suggest our customers to use the new RadChartView components instead of the old RadChart because the new control is much faster, it solves many limitations the old component has, and it is very flexible and easy to set up. You can read about the differences between the controls in theRadChart vs. RadChartView help article.
As I can see from the attached picture the horizontal axis of your chart contains DateTime values. With the new chartview you can use the DateTimeContinuousAxis which is designed to work with such data. The date time axis has few properties which you can use to control the arraignment of its labels. With theMajorStep property you can define the step between two adjacent ticks on the axis. TheMajorStepUnit defines the custom major step of the axis (Day, Month, Year, etc.). You can take a look at the Axis help article that describes most of the axes properties. In addition I attached a sample project that demonstrates RadCartesianChart with a DateTimeContinuousAxis.
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